2,5-distyrylpyrazines

ABSTRACT

A reactive 2,5-distyrylpyrazine compound having the formula &lt;IMAGE&gt;  (I)    &lt;IMAGE&gt;  wherein X is COCH3 or H, and a polymer obtained from the compound.

The present invention relates to a novel diolefinic compound having asubstituent at the 4-position of 2,5-distyrylpyrazine and a process forits preparation.

The present invention relates to a novel linear polyamic acid or linearpolyimide having 2,5-distyrylprazine units in its main chain and aprocess for preparing the same.

STATEMENT OF PRIOR ARTS

Diolefinic compounds, such as 2,5-distyrylpyrazine, having a rigidmolecular structure, are known to undergo solid-state polymerization togive a highly crystalline polymer with a high molecular weight. But nocompound having an amino group at the 4-position of a phenyl ring of2,5-distyrylpyrazine has ever been disclosed.

An aromatic polyimide has excellent mechanical, electrical, physical,and chemical properties and is widely used for electronics, electricfield, precision instruments, etc., in the form of a film, varnish, andmolded article. A linear aromatic polyimide has hitherto beensynthesized by allowing an aromatic tetracarboxylic dianhydride, such aspyromellitic dianhydride, benzophenonetetracarboxylic anhydride ordiphenyl ether tetracarboxylic dianhydride, to act on an aromaticdiamine, such as phenylenediamine, diaminodiphenyl,diaminodiphenylmethane, diaminodiphenyl ketone, diaminodiphenyl ether,diaminodiphenyl thioether or diaminodiphenyl sulfone, to prepare apolyamic acid and then subjecting the polyamic acid to thermal ringclosure.

However, the aromatic polyamic acid and aromatic polyimide comprising2,5-bis(4-aminostyryl)pyrazine as an aromatic diamine componentaccording to the present invention, namely, a polyamic acid and apolyimide having a rigid molecular skeleton and containing2,5-distyrylpyrazine units having high photoreactivity in its polymermain chain have not been known.

SUMMARY OF THE INVENTION

The present inventor has made extensive and intensive studies on a2,5-distyrylpyrazine compound having an amino group at the 4-positionthereof and, as a result, have synthesized a novel compound, i.e.,2,5-bis(4-acetaminostyryl)pyrazine and 2,5-bis(4-aminostyryl)pyrazine,which has led to the completion of the present invention.

Specifically, the present invention provides a 2,5-distyrylpyrazinecompound represented by following structural formula (I) ##STR2##wherein X is COCH₃ or H, i.e., 2,5-bis(4-acetaminostyryl)pyrazine and2,5-bis(4-aminostyryl)pyrazine respectively represented by followingstructural formulae (IV) and (V): ##STR3##

The compound of the present invention can be prepared via the followingsynthetic pathway. Specifically, 2,5-bis(4-acetaminostyryl)pyrazine (IV)can be prepared by allowing p-acetaminobenzaldehyde to act on2,5-dimethylpyrazine in the presence of a condensing agent.2,5-bis(4-aminostyryl)pyrazine (V) can be prepared by deacetylation of2,5-bis(4-acetaminostyryl)pyrazine under acidic conditions. ##STR4##

In above-described formula (1), letter A designates a condensing agentcomprising polyphosphoric acid, acetic anhydride, sulfuric acid, benzoicanhydride, zinc chloride, or a mixture thereof. However, the condensingagent is not limited to these only, and any compound having acondensation activity can be used. Letter B designates an acid catalystsuch as hydrochloric, sulfuric, p-toluenesulfonic, or phosphoric acid.However, the acid catalyst is not limited to these only, any Bronstedacid can be used.

The compound of the present invention is a bifunctional monomer having ahighly reactive amino group and therefore is useful for all classes ofpolymers prepared from a starting monomer comprising a diaminecomponent. For example, the compound of the present invention is usefulas a monomer for polyamide, polyimide, polysulfonamide, polyurea,polyamine, etc., i.e., a polymer having an amide, imide, sulfonamide,urea or amino bond and a polymer having a combination of these bonds.

Further, the compound of the present invention forms an adduct having acyclobutane ring through [2+2] photocycloaddition. Moreover, thecompound of the present invention has such a property that thecyclobutane ring or pyrazine ring is photocleaved upon being exposed toshort-wavelength light.

Therefore, the compound of the present invention is useful as aphotoreaction reagent or an optical recording material which utilize theabove-described properties. Since the compound of the present inventionper se is a fluorescent substance, it is suitable also for use as abrightener and an analytical or measuring reagent as a photoreactivefluorescent substance.

The present inventor has made extensive and intensive studies on anaromatic polyamino acid and an aromatic polyimide having a rigidmolecular structure and then photoreactivity and comprising2,5-bis(4-aminostyryl)pyrazine as a diamine component and, as a result,have accomplished the invention of the present application.

Specifically, the present invention provides a polymer represented byfollowing general formula [XI] more particularly an aromatic polyamicacid represented by following general formula [XIV] and an aromaticpolyimide represented by following general formula [XV]: ##STR5## Ar isan aromatic tetrafunctional residue and n is an integer of 2 or more:##STR6##

The polymer of the present invention can be prepared via the followingsynthetic pathway.

Specifically, 2,5-bis(4-aminostyryl)pyrazine represented by formula[XII] is reacted with a tetracarboxylic dianhydride represented byfollowing general formula [XIII] to prepare a polyamic acid of formula[XIV].

2,5-Bis(4-aminostyryl)pyrazine can be prepared via the followingsynthetic pathway. Specifically, p-acetaminobenzaldehyde (b) is allowedto act on 2,5-dimethylpyrazine (a) in the presence of a condensing agentto prepare 2,5-bis(4-acetaminostyryl)pyrazine (c). The2,5-bis(4-acetaminostyryl)pyrazine can be deacetylated under acidicconditions to prepare 2,5-bis(4-aminostyryl)pyrazine [XII]. ##STR7##

In above-described reaction formula (1), letter A designates acondensing agent comprising polyphosphoric acid, acetic anhydride,sulfuric acid, benzoic anhydride, zinc chloride, or a mixture thereof.However, the condensing agent is not limited to these only, and anycompound exhibiting a condensation activity can be used. Letter Bdesignates an acid catalyst such as hydrochloric, sulfuric,p-toluenesulfonic or phosphoric acid. However, the acid catalyst is notlimited to these only, and any Bronsted acid can be used. Then apolyamic acid of formula [XIV] is subjected to thermal ring closure toprepare a polyimide of formula [XV].

The synthesis of a polyamic acid and a polyimide through a reaction of2,5-bis(4-aminostyryl)pyrazine ##STR8## with a tetracarboxylicdianhydride represented by above-described reaction formula (2) can beconducted under the same conditions as those of the synthesis of usualpolyamides. Specifically, a polymer in a film form can be prepared asfollows. 2,5-Bis(4-aminostyryl)pyrazine is dissolved in a polar solvent,e.g., dimethylacetamide (DMAc), and a tetracarboxylic dianhydride in amolar amount equal to that of this diamine is added thereto mixing toprepare a polyamic acid solution. This solution is cast and vacuum driedto prepare a polyamic acid film. This film is heat treated for thermalring closure, thereby preparing a polyimide film.

In the process of the present invention, the aromatic tetracarboxylicdianhydride for use as a starting material in the synthesis of apolyamic acid and a polyimide may be those usually employed in thesynthesis of an aromatic polyimide. Especially the aromatictetracarboxylic dianhydride may be one represented by above describedgeneral formula (XIII) wherein Ar is a member selected from thefollowing aromatic tetrafunctional residues. Further the aromatictetracarboxylic dianhydride may be a mixture of two or more of thesedianhydrides. ##STR9##

Preferred examples of the tetracarboxylic dianhydride includepyromellitic dianhydride, 2,3,6,7-naphthalene tetracarboxylicdianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride,3,3',4,4'-diphenyltetracarboxylic dianhydride,3,3',4,4'-benzophenonetetracarboxylic dianhydride, and3,3',4,4'-diphenyl ether tetracarboxylic dianhydride.

Although the degree of polymerization of the polyamic acid and polyimideaccording to the present invention is not well-defined, the value of nin above-described general formulae [XIV] and [XV] determined from thevalue of the reduced viscosity of a solution of the polyamic acid is 50or more.

The polyamic acid and polyimide according to the present invention areeach a polymer having resistance to heat and usual organic solventscomparable to various conventional aromatic polyamic acids and aromaticpolyimides. Interestingly, the polyimide of the present invention issoluble in sulfuric acid in which common aromatic polyimides areinsoluble, because it has a pyrazine residue in its main polymer chain.

The polyamic acid and polyimide prepared according to the presentinvention can be utilized as a coating material, film, molding resin,laminate, and composite material. Further, the polyamic acid andpolyimide according to the present invention are each a polymer having ahigh modulus of elasticity because they each have a 2,5-distyrylpyrazineunit comprising a rigid molecular skeleton in its main chain. Moreover,since the polyamic acid and polyimide according to the present inventioneach have photoreactive double bonds in its main chain, exposure tolight brings about [2+2] cycloaddition (said photoreaction bringingabout the formation of a three-dimensional structure and the cleavage ofthe conjugated system). Therefore, the polyamic acid and polyimideaccording to the present invention can be used for an isotropicpolyimide having a high modulus of elasticity, a photosensitive polymer,an optical display material, an optical recording material, or the likeby taking advantage of this photoreactivity.

Further, the polyamic acid and polyimide according to the presentinvention have a pyrazine residue in its main chain. This pyrazineresidue imparts a number of interesting characteristics to the polymer.That is, the pyrazine residue is a hydrophilic and basic functionalgroup and can be easily protonated and quaternized.

Therefore, the polyamic acid and polyimide according to the presentinvention can be applied to a separative membrane, a chelating resin,and an ion exchange resin by taking advantage of the hydrophilic andbasic properties of the pyrazine residue. Further, it is possible to usethe polyamic acid and polyimide according to the present invention asanalytical and measuring reagents.

BRIEF DESCRIPTION OF ATTACHED DRAWING

FIGS. 1 and 2 are respectively charts of an infrared absorption spectrumand a 300 MHz ¹ H-NMR spectrum of 2,5-bis(4-acetaminostyryl)pyrazineprepared in Example 1, and

FIGS. 3 and 4 are respectively charts of an infrared absorption spectrumand a 300 MHz ¹ H-NMR spectrum of 2,5-bis(4-aminostyryl)pyrazineprepared in Example 2.

FIGS. 5 and 6 are charts of infrared absorption spectra of aromaticpolyimides prepared in Examples 4 and 5, respectively, and

FIGS. 7 and 8 are thermogravimetric curves of aromatic polyimidesprepared in Examples 4 and 5, respectively.

[EXAMPLES]

The present invention will now be described in more detail withreference to the following Examples which should not be construed aslimiting the scope of the present invention.

EXAMPLE 1 Synthesis of 2,5-bis(4-acetaminostyryl)pyrazine ##STR10##

10.8 g (0.1 mol) of 2,5-dimethylpyrazine, 36.0 g (0.2×1.1 mol) ofp-acetaminobenzaldehyde, and 1.0 g of ZnCl₂ were placed in around-bottomed flask, and allowed to react on an oil bath at 180° C. for4 hr and then at 200° C. for 2 hr. 200 ml of dimethylacetamide (DMAc)was added to the reaction mixture, followed by reflux for 10 min. Thereaction mixture was transferred to an Erlenmeyer flask through a filterpaper. The same procedures were repeated by making use of 200 ml of DMAcand finally 100 ml of DMAc. The crystals thus precipitated werecollected by filtration and recrystallized from DMAc.

Amount of product: 23.6 g. Yield: 59.3%.

    ______________________________________                                        Results of elementary analysis                                                C (%)       H (%)         N (%)                                               calculated                                                                            found   calculated                                                                              found calculated                                                                            found                                 ______________________________________                                        72.34   72.59   5.57      5.48  14.06   14.06                                 ______________________________________                                    

An infrared absorption spectrum (KBr disk method) and a 300 MHz ¹ H-NMRspectrum [solvent: dimethyl sulfoxide-d₆ (DMSO-d₆), internal reference:tetramethylsilane (TMS)] 2,5-bis(4-acetaminostyryl)pyrazine are shown inFIGS. 1 and 2, respectively.

IR: (KBr disk method): 3307, 1664, 1592, 1535, 1411, 1367, 1321, 1268,973, 823 cm⁻¹.

¹ H-NMR (300 MHz; DMSO-d₆): δ2.07 (s, 6H), δ7.2-7.3 (d, 2H), δ7.5-7.8(m, 10H), δ8.70 (s, 2H), δ9.99 (s, 2H) ppm.

EXAMPLE 2 Synthesis of 2,5-bis(4-aminostyryl)pyrazine ##STR11##

10.0 g of 2,5-bis(4-acetaminostyryl)pyrazine prepared in Example 1 wasrefluxed together with 100 ml of concentrated hydrochloric acid for 6hr. The reaction mixture was allowed to cool and filtered. The collectedproduct was dispersed in 200 ml of water and then alkalinized to astrongly alkaline state with sodium hydroxide. The product was collectedby filtration, recrystallized from DMAc containing a small amount ofwater, and recrystallized from DMAc.

Amount of product: 5.6 g.

Yield: 71.0%.

    ______________________________________                                        Results of elementary analysis                                                C (%)       H (%)         N (%)                                               calculated                                                                            found   calculated                                                                              found calculated                                                                            found                                 ______________________________________                                        76.41   76.38   5.77      5.63  17.82   17.62                                 ______________________________________                                    

An infrared absorption spectrum (KBr disk method) and a 300 MHz ¹ H-NMRspectrum [solvent: DMSO-d₆, internal reference: TMS] of2,5-bis(4-aminostyryl)pyrazine are shown in FIGS. 3 and 4, respectively.

IR: (KBr disk method): 3318, 3197, 1596, 1515, 1483, 1286, 1178, 1151,1027, 975, 817 cm⁻¹.

¹ H-NMR (300 MHz; DMSO-d₆): δ5.42 (s, 4H), δ6.5-6.7 (d, 4H), δ6.9-7.1(d, 2H), δ7.3-7.5 (d, 4H), δ7.5-7.7 (d, 2H), δ8.54 (s, 2H) ppm.

EXAMPLE 3 (Evaluation of Photoreactivity)

The photoreactivity of crystalline 2,5-bis(4-acetoaminostyryl)pyrazineand 2,5-bis(4-aminostyryl)pyrazine prepared in Examples 1 and 2 wasexamined. The photoreactivity was evaluated by exposure to light from a100-W high-pressure mercury lamp at room temperature for 24 hr. In theIR spectrum, there was observed a decrease in the absorption peakassignable to an olefin, suggesting the occurrence of a photoreaction.Further, these compounds showed fluorescence having a bluish purplecolor and brought about a reaction upon being exposed to light insolution. The reaction was confirmed by the thin layer chromatography.

EXAMPLE 4

0.314 g (0.001 mol) of 2,5-bis(4-aminostyryl)pyrazine was placed in anErlenmeyer flask equipped with a cap and containing a stirring bar todisperse it in 4.0 ml of DMAc. Then, 0.332 g (0.001 mol) of powderypyromellitic dianhydride (PMDA) was added thereto in portions. Themixture was stirred at room temperature for 12 hr. The resultant viscouspolyamic acid solution was sampled to measure the reduced viscosity in aconcentration of 0.2 g/dl. Since the polyamic acid has a high viscosity,4.0 ml of DMAc was further added thereto and the mixture was stirred.The resultant solution was cast on an aluminum foil, heated and dried at80° to 100° C. in vacuo, thereby preparing a polyamic acid film. Thepolyamic acid on the aluminum foil was dried and dehydrated at 220° C.for 10 hr in vacuo, and then cooled. The cooled aluminum foil wastreated with a diluted hydrochloric acid, washed with water andair-dried to recover polyimide film.

An infrared absorption spectrum of this aromatic polyimide is shown inFIG. 5. Supposedly the reaction proceeds as shown in the followingreaction formula: ##STR12##

EXAMPLE 5

A polyamic acid and a polyimide film were prepared in the same manner asthat of Example 4 except that 3,3',4,4'-benzophenonetetracarboxylicdianhydride (BTDA) was used as the tetracarboxylic dihydride.

An infrared absorption spectrum of the polyimide thus prepared is shownin FIG. 6. Presumably the reaction proceeds via the same pathway as thatof Example 4.

EXAMPLE 6 Heat Stability (TGA) of Polyimide

A polyimide film was applied to thermogravimetric analysis, and heatstability thereof was determined from a 10% weight loss temperature anda pyrolysis curve. The TGA curves are shown in FIGS. 7 and 8. The 10%weight loss temperatures in air and in nitrogen are shown in Table 1.FIG. 7 is a TGA curve of a polyimide prepared from PMDA (Example 4),while FIG. 8 is a TGA curve of a polyimide prepared from BTDA (Example5). In the drawings, a solid line represents the results of measurementin the air, while a dotted line represents the results of measurement innitrogen.

                  TABLE 1                                                         ______________________________________                                                   10% weight loss temperature (°C.)                           ______________________________________                                        Ex. 4      air   456                                                          (PMDA)     N.sub.2                                                                             565                                                          Ex. 5      air   465                                                          (BTDA)     N.sub.2                                                                             525                                                          ______________________________________                                    

EXAMPLE 7 Solubility of Polyimide

The solubility of polyimide PMDA and polyimide BTDA respectivelyprepared from PMDA and BTDA is shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Polyimide                                                                                   polyimide A  polyimide B                                        solvent       PMDA (A)     BTDA (B)                                           ______________________________________                                        sulfuric acid easily soluble                                                                             easily soluble                                     hydrochloric  swelling     swelling                                           acid                                                                          trifluoro-    swelling     swelling                                           acetic acid                                                                   dimethyl-     insoluble    insoluble                                          formamide                                                                     m-cresol      insoluble    insoluble                                          hexafluoro-   insoluble    insoluble                                          2-propanol                                                                    ______________________________________                                    

The color of the polyimide PMDA turned from reddish purple to deepreddish purple in hydrochloric acid and trifluoroacetic acid. In thesame solvents, the color of the polyimide BTDA turned from yellow todeep reddish purple.

EXAMPLE 8 Photoreactivity of Polyimide

Polyimide films respectively prepared from PMDA and BTDA were exposed tolight from a 500-W high-pressure mercury lamp for 24 hr, which broughtabout a decrease in an intensity of the infrared absorption peakassignable to an olefin.

I claim:
 1. A 2,5-distyrylpyrazine compound represented by the followingstructural formula (I): ##STR13## wherein X is COCH₃ or H.
 2. The2,5-distyrylpyrazine compound according to claim 1, wherein X is COCH₃.3. The 2,5-distyrylpyrazine compound according to claim 1, wherein X isH.